This invention relates to an apparatus for emulating a microprocessor and particularly for debugging software and hardware of electronic instrument including a microprocessor.
There are some cases where it is needed to read out or modify stored matter contained in a memory being externally or internally equipped with the microprocessor employed in the electronic instrument for storing programs and data, and in a register thereof for temporarily storing various data. The operation of reading out and modifying are generally performed by utilizing an interrupt signal which is a kind of a control signal included in the microprocessor itself and a signal for temporally stopping the operation thereof.
To confirm that the stored matter in the memory and the register has had a predetermined value or not, in a conventional emulator, the stored matter has been read out and if it has not been the predetermined value, the stored matter has been correctively modified partially, thereafter a following program has been proceeded. Such a program as abovementioned for reading out and modifying has been involved in the emulator and has been different from a program included in the system under test.
To read out and modify as above described, in the conventional emulator, an interrupt request signal has been fed from the emulator to an interrupt terminal of the microprocessor included in the system under test. When the emulator has received a response signal of the microprocessor of the system responding to the interrupt request signal, a bus of the microprocessor employed in the system under test has been exchanged to a bus of the emulator, synchronized with the response signal. Thus, a program of the emulator for reading out and modifying has been performed in the system under test.
However, in case the program of the system under test has been programmed to inhibit any interrupt signal, the interrupt signal from the conventional emulator has not been accepted thereby. And, in case there has been no interrupt signal terminal in the microprocessor of the system under test, the interrupt request signal has not been able to be fed thereto. Therefore, the program from the conventional emulator for reading out and modifying the stored matter in the register and the memory in the system under test has not been performed.